1. Field of the Invention
This invention relates to a method for forming a thin film, particularly to a method for forming a thin film suitable for a secondary battery field usable for mobile electronic device and electric automobiles.
2. Related Art Statement
So far, a sol-gel method, a CVD method or a PVD method is employed as a thin film-forming method. These methods require multistage process including a heating process, a high vacuum condition, or a high energy condition accompanied with a substrate-heating process or a plasma-generating process. Therefore, those methods require large scale and complicate apparatus, resulting in large cost and complicate operationality in use.
Moreover, the above high energy condition runs counter to global environmental protection, resource saving and energy saving. Therefore, a new thin film-forming method without the above high energy condition has been desired.
It is an object of the present invention to provide a new thin film-forming method not including a high energy condition due to firing, heating or plasma generation.
This invention relates to a method for forming a thin film (herein-after, often called as a xe2x80x9cfirst thin film-forming method) comprising the steps of:
setting an anode electrode and a cathode electrode in a reactive solution,
flowing the reactive solution in between the anode electrode and the cathode electrode at a given flow rate, and
applying a given voltage between the anode electrode and the cathode electrode, thereby to synthesize a compound thin film including the components of the reactive solution and the anode electrode on the anode electrode.
This invention also relates to a method for forming a thin film (hereinafter, often called as a xe2x80x9csecond thin film-forming method) comprising the steps of:
setting an anode electrode and a cathode electrode in a reactive solution,
flowing the reactive solution in between the anode electrode and the cathode electrode at a given flow rate, and
applying a given voltage between the anode electrode and the cathode electrode, thereby to synthesize a compound thin film including the components of the reactive solution and the anode electrode on a given substrate arranged in the flow direction of the reactive solution.
The inventors related to the present invention have been intensely studied for developing a new thin film-forming method not including a high energy process. As a result, they have found out surprisingly that when a reactive solution incorporating a component of a desired thin film is flown in between an anode electrode and a cathode electrode to which a given voltage is applied, the desired compound thin film including the component of the reactive solution and another component of the anode electrode is synthesized directly on the anode electrode. Then, they have also found out that when the anode electrode and the cathode electrode are set in a static reactive solution and a given voltage is applied between the anode electrode and the cathode electrode, the compound thin film is not synthesized on the anode electrode.
The first thin film-forming method of the present invention is made on the discovery of the above phenomenon. The first thin film-forming method enables the desired compound thin film to be formed directly on the anode electrode without the high energy condition including the substrate-heating process and the plasma generation.
Moreover, the inventors have found out that if the flow rate of the reactive solution and the voltage applied between the anode electrode and the cathode electrode are controlled appropriately, the compound thin film composed of the components of the reactive solution and the anode electrode can be synthesized on a given substrate which is arranged in the flow direction of the reactive solution.
The cause of the thin film formation on the given substrate may be considered as follows: That is, the reactive solution erodes and melts the superficial parts of the anode electrode, and thus, the melted anode electrode material and the reactive solution arrive at and synthesized on the substrate.
The second thin film-forming method of the present invention is made on the discovery of the above phenomenon. The second thin film-forming method enables the compound thin film to be formed on the given substrate without the high energy condition including the substrate-heating process and the plasma generation.